1. Field of the Invention
The present invention relates generally to devices for repairing pipes. In particular, the present invention relates to an apparatus for repairing and providing a temporary seal around piping in an internal core spray-system of a nuclear reactor.
2. Description of the Related Art
The boiling water nuclear reactor industry has experienced extensive cracking in certain internal reactor parts. Among these parts is the core spray piping, which is presently being repaired or reviewed on most nuclear reactor plants.
The core spray piping functions to bring core spray flow through the core shroud from a source external to the reactor pressure vessel. The piping enters the vessel through a safe end above the shroud and immediately goes into a tee that divides the flow into two pipes. Each pipe curves around the interior of the vessel until it reaches a vertical section, and is supported with at least one support along the path. The vertical section extends down to the shroud where the piping enters through another safe end and terminates in a tee located in the sparger at the top of the shroud. There are typically two spray piping systems per reactor vessel which serve four half-circle spray spargers in the shroud. In most existing systems, the piping includes steel pipes and welded couplings which are susceptible to intergranular stress corrosion cracking due to the oxidizing environment of the reactor, welding process and the stagnant water typically present in the pipes.
The vertical section of piping typically includes a welded pipe coupling assembly immediately outside of the core shroud. This section of piping has been particularly prone to cracking, which can result in leakage or even structural damage to the internal core spray piping.
U.S. Pat. No. 5,735,551 issued to Whitman et al. discloses an L-shaped pipe repair apparatus for repairing the welded pipe assembly immediately outside of the core shroud. This apparatus includes first and second housings that are bolted together over the pipe to be repaired. A first seal is mounted within the housing assembly to seal against an outer circumferential surface of the pipe, and a second seal is mounted at an end of the housing assembly to seal against a wall of the core shroud. The housing assembly is retained in place against the outer wall of the core shroud by a threaded rod extending through the wall of the shroud or by a spring fixture that reacts against the wall of the reactor vessel.
The pipe repair apparatus of Whitman et al. suffers from the following disadvantages. First, the apparatus must be sized and machined precisely to fit the pipe to be repaired. The apparatus is not designed to accommodate differences in the outside diameters of the pipes. Second, the apparatus does not prevent cracks in the existing pipe from continuing to propagate and allowing the pipe to pull apart. Third, the L-shaped design of the apparatus is expensive to manufacture, difficult to install, and limits the versatility of the apparatus. The L-shaped design has limited usefulness in many cases since the cracks and leaks in the piping tend to occur in the welded couplings at varying distances above the elbow. The L-shaped design also prevents the apparatus from being used on straight sections of piping that are not adjacent to an elbow.
U.S. Pat. No. 5,737,380 issued to Deaver et al. discloses a replacement core spray line assembly for a nuclear reactor. This core spray line assembly provides a permanent repair of leaking or cracked core spray lines by replacing the lines with new pipes and connectors. This assembly does not provide a temporary repair assembly that can be quickly applied over existing piping as cracked conditions are found at a nuclear reactor plant.
Thus, there is a need for an improved apparatus that can be applied over existing piping to provide a temporary repair for cracked and/or leaking pipes and couplings in a boiling water nuclear reactor plant.